George's post from mercedes113.org:
Now that I think about it more, the problem I had was that the turn signals wouldn't stay on, but maybe the problems are related. What happened is this: there are two little metal rockers that pivot on little studs. The studs are part of the main switch casting. I think the springs attach at one end of the rockers, the other end has a small roller on it. The ends of the cast-on studs were originally mashed out like a rivet head to retain the rockers. There is also a small washer between the rocker and the mashed stud head. In my case, the mashed stud heads had broken off. The rockers and washers stayed on the studs, but since they were no longer tightly held, the rockers could twist, which got the rollers out of alignment, and this caused the problem.
The fix was to drill down through the center of the studs, tap the holes and install #4-40 round-head machine screws. The screw heads replace the mashed stud heads and keep the rockers from twisting. I left the washers out and had to grind the screw heads down so that the mechanism would clear them, and had to recut the screwdriver slot with a dremel and cut-off wheel. Used a tiny bit of lock-tite to hold the screws in place, making sure not to get any lock-tite into the mechanism. The screws stuck out on the other side of the casting, a few seconds with the dremel and cut-off disc took care of them after lock-titing. Work carefully, and reassemble and test before lock-titing, and make sure no little pieces of metal (or a stray washer) are left in the mechanism, they cause short-circuits and blow fuses (learned that the hard way, of course). Last, use 1 inch long 4-40 screws, they have to be cut off anyway and longer screws are easier to work with.
Hope this is helpful, my turn signals have been working well since doing this.
Also, check out this old thread in our own forum, very informative!
http://index.php?topic=554Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420